Wireless communications systems refer generally to any telecommunications system which enables wireless communication between its users and a network. In mobile communications systems users are capable of moving within the coverage area of the network. A mobile communications network can be divided into two main parts, which are the radio access network and the core network. Examples of radio access networks are GSM (Global System for Mobile telecommunications) and its enhancements EDGE (Enhanced Data rates for GSM Evolution), GPRS (General Packet Radio Service), GERAN (GPRS EDGE Radio Access Network) which is a GSM/GPRS based 3rd generation radio network, IS-95 (Interim Standard), DS-41, cdma2000 (code division multiple access), WCDMA UTRAN (Wideband CDMA UMTS Terrestrial Radio Access Network; Universal Mobile Telecommunications System). Examples of core networks are: GSM, GPRS, IS-41 (also called ANSI-41) and the 3rd generation evolutions of these core networks.
The current trend in standardization is to find possibilities to connect one radio access network to various core network types and vice versa. One good example of this kind of activity is the 3GPP specification work where WCDMA UTRAN connectivity will be specified to both GSM-based (incl. GPRS) and IS-41 based core networks. The present invention can be used in different mobile communications systems and is not limited to any particular radio access network or core network. In the following, the invention is described by way of example with reference to UMTS, more specifically to the UMTS system being specified in the 3rd generation partnership project 3GPP, without restricting the invention to it.
The specifications of many second generation and most third generation cellular radio systems give support for establishing real time (RT) and non-real time (NRT) services between mobile terminals and base stations. RT services are used for time-critical applications like speech and real time video, while NRT applications usually convey data like e-mails or downloaded files. It is characteristic to RT services that a user (be it a human user or a process) notices immediately if there are inappropriate delays or breaks in the radio bearer through which the service is provided.
In cellular radio systems it often happens that a radio connection between a user terminal and a serving base station is temporarily lost due to interference or unfavorable signal propagation conditions. In most cellular radio systems there have been determined arrangements for re-establishing lost connections rapidly so that the incident might pass unnoticed to the user or at least the inconvenience caused would be as small as possible. As an example we will consider the re-establishment procedures defined for RRC (Radio Resource Control) connections in the 3GPP (Third Generation Partnership Project) specification numbers TS25.331, TS25.302, TS25.321 and TS25.322 which are published by the ETSI (European Telecommunications Standard Institute) and incorporated herein by reference.
According to said prior art document, when a mobile terminal (or a UE; user equipment) loses the radio connection due to e.g. radio link failure while it is in a so-called CELL_DCH state, the mobile terminal may initiate a new cell selection by transiting into a so-called CELL_FACH state and requesting re-establishment of an RRC connection. The acronyms DCH and FACH come from Dedicated CHannel and Forward Access CHannel and said states are characterized by that the mobile terminal uses primarily these channels. After having detected the loss of a radio connection the mobile terminal starts a timer which in said prior art document is referred to as the timer T314, or the ‘re-establishment’ timer. If the mobile terminal finds itself to be within an “in service area”, where connection re-establishment is possible, it stops the timer T314 and transmits a message known as the RRC CONNECTION RE_ESTABLISHMENT REQUEST on the uplink CCCH or Common Control CHannel. However, if the timer T314 makes it to expiry before the mobile terminal finds itself to be within an “in service area”, the mobile terminal must enter an RRC-idle mode where active communication with base stations is not possible.
The value of the timer T314 may be anything between 0 and 4095 seconds. An RNC (Radio Network Controller) sets the timer value and sends it to the mobile terminal in some dedicated control message like the known RRC Connection Setup, Radio Bearer Setup, Radio Bearer Release, Radio Bearer Reconfiguration, Transport channel reconfiguration, Physical Channel Reconfiguration and RRC Connection Re-establishment messages. In other words, the timer value may be specific to the mobile terminal in question and it may even be changed during a RRC connection, depending e.g. on the current service configuration of the mobile terminal.
The problem with the prior art arrangement is its inflexibility regarding different types of services, e.g. real time vs. non-real time services. Due to its nature an RT connection does not tolerate long delays or breaks, so a relatively small value, in the order of seconds, should be selected for the expiry of the timer T314 (or other timer used for a similar purpose). It should even be possible to “turn off” the re-establishment possibility for RT bearers, meaning that if UE loses the radio connection, the RT bearers are released (locally in UE and in UTRAN) immediately. On the other hand NRT connections are much more tolerable and could withstand temporary delays in the order of minutes or even tens of minutes. If the mobile terminal has active radio bearers related both to real time and non-real time connections in use at the moment of radio link failure, at least one of these suffers from an inadequately selected expiry value for the re-establishment timer.
In addition to the real time/non-real time division it is possible to group the services conveyed over radio bearers into other kinds of groups that also have different requirements regarding the timing of connection re-establishment.